Magnetic centering device and support means for post deflection control of electron beams



p 1967 s. L. REICHES ETAL.

MAGNETIC CENTERING DEVICE AND SUPPORT MEANS F0 POST DEFLECTION CONTROL OF ELECTRON BEAMS Filed July 26, 1963 2 Sheets-Sheet l Inventors 501 L. Reickes Lindsleg/ Clarke 33 $1 2 6 7 .fl' iornegs Aprll 1967 s. 1.. REICHES ETAL 3,316,433

MAGNETIC CENTERING DEVICE AND SUPPORT MEANS FOR POST DEFLECTION CONTROL OF ELECTRON BEAMS Filed July 26, 1963 llrwencors S L.R k Lind leg Clc n ie 5 49204 2 ai /Mics? United States Patent Otiice 3,316,433 Patented Apr. 25, 1967 3,316,433 MAGNETIC CENTERING DEVICE AND SUPPORT MEANS FOR POST DEFLECTION CONTROL OF ELECTRON BEAMS Sol L. Reiches and Lindsley Clarke, both Park Products Co., 566 N. Eagle St., Geneva, Ohio 44041 Filed July 26, 1963, Ser. No. 297,885 3 Claims. (Cl. 313-77) The present invention relates to an improved mechanism for use with a wide angle color television cathode ray tube for adjustably accommodating variations in ambient magnetic field, tube construction tolerances, and the like.

In one form of color television display mechanism, a cathode ray tube is provided with a plurality of electron guns, usually three. These are disposed in spaced relation with the axis of the tube, preferably parallel thereto and forming equally spaced elements of a cylinder coaxial with the tube. The viewing screen has a plurality of complementary arrays of phosphor dots, one array for each of the colors to be reproduced. An apertured screen or shadow mask is interposed between the electron guns and the viewing screen. It has a single set of holes in the same geometric configuration as each array of phosphor dots. The respective phosphor dots of each array are so located in relation to the positions of the openings in the shadow mask that when the electrons travel their intended course from each electron gun to the viewing screen they strike (that is, illuminate) only those of the phosphor dots that produce the color intended to be reproduced by that gun. The ray beam of each gun is time modulated in accord with the color information required on the viewing screen for that particular color. Color image display mecha- 'nisms of this type are, in one form, called the shadow mask type of color image display. The net effect is to produce a plurality of, registered images, usually three, in dot patterns that are merged in the eye of the observer to produce the illusion of a continuous tone color image while the ray beams are swept over the viewing screen in unison.

Effective operation of a television color image display mechanism of the above type requires that the electrons from the respective electron guns approach the viewing screen from predetermined paths of travel. Any deviations from the intended paths will cause the electrons of the gun involved either to produce no image (by striking the screen where there are no phosphor dots) or to produce an image of the wrong color. In either event the fidelity of the color image is impaired.

A number of unavoidable effects tend to cause departures of the paths of travel of the electron beams from the intended paths. One is the earths magnetic field, which varies to some degree from place to place and also varies in its orientation. Consequently, merely repositioning the color television receiving set can entail a loss of color fidelity by varying the influence of the earths magnetic field. Abnormalities inambient magnetic field can also cause departures from color purity for similar reasons. In addition, unavoidable tolerances in tube manufacture and receiver construction must be accommodated, giving rise to a further need for some form of control. For these and other reasons it is important in a color television system of the above type to provide some means whereby the patterns of travel of the cathode electron beams may be adjusted.

The present invention is particularly directed to socalled 90 color television cathode ray tubes, that is tubes of relatively short axial length in relation to the size of the viewing screen and therefore requiring wide angle sweep of the order of 90 degrees or more. In tubes of this kind it has been found that the necessary control can be. achieved through the medium of adjustable diametrically magnetized magnets having relatively large diameters in relation to the diameter of the cathode ray tube neck, and yet so organized as to be effective on the ray beams over a relatively short axial distance of the tube. More particularly, in accordance with the preferred form of the present invention, a pair of diametrically magnetized ring magnets of about 8 inches diameter are telescoped over the neck of the tube and positioned adjacent the bell of the tube. These rings are effective to produce a relatively uniform field within the tube neck in the plane of the rings which field may be adjusted as to orientation and intensity without substantial impairment of its uniformity. Further in accordance with the present invention a magnetic shield, preferably conical, is disposed between the magnet rings and the adjacent portion of' the bell of the tube. Also, in accordance with the preferred form of the present invention, a saturable sleeve is located inboard of the adjustable magnetized rings, the saturable ring being of such dimensions and magnetic characteristics as to saturate when the rings are adjusted to give a significant proportion of the maximum field they are capable of producing. Through this mechanism it is possible to provide a magnetic field cross-wise of the tube and of adjustable orientation and intensity, the intensity being variable down to substantially zero field. The field is effective over only a short axial distance of the tube. The field pattern possible by this mechanism, it has been found, is such as to permit shifting of the ray beams in substantially equal fashion throughout their entire scanning cycles and thus compensate at all parts of the image in a uniform fashion. In actual practice, the apparatus has been found capable of accommodating variations in ambient magnetic field, including the earths field, tube constructional tolerances, and the like to provide a high degree of fidelity of color reproduction.

It is therefore a general object of the present invention to provide an improved adjustable mechanism for providing color purity in a color television image display mechanism using a wide angle color cathode ray tube.

A further and more detailed object of the present invention is to provide an improved adjustable mechanism for providing color purity in a color television image display mechanism using a wide angle color cathode ray tube and wherein adjustable elements are effective to shift the cathode ray beams substantially uniformly at all points of their scanning raster in such fashion as to overcome the effects of tube constructional tolerances, variations in ambient magnetic field, and the like over the entire area of the image.

. Another object and advantage of the present invention is to provide a mechanism capable of adjusting the ray beams of a color cathode ray tube by the application of a relatively uniform magnetic field having adjustable intensity and orientation but effective over only a short axial distance.

Still another object of the present invention is to provide a mechanism of. the foregoing type which takes advantage of the ray beam deflection mechanism to prevent undesired reactions between the ray beams and the adjustable elements.

Yet another object of the present invention in one form is to provide a mechanism of the foregoing type wherein the field may be adjusted down to substantially zero value.

Further and additional objects of the present invention are to provide a structure meeting the foregoing objects and which is simple in construction, reliable in operation, is readily adjusted, and in other respects is particularly suited to practical use in home color te evision receivers.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic axial view illustrating a display apparatus for use in the present invention;

FIGURE 2 is a fragmentary view in cross-section of a portion of the evidence of a color cathode ray tube, the core of a deflection yoke, and the ray beam adjusting apparatus all as constructed in accordance with the preferred form of the present invention;

FIGURE 3 is a cross-sectional view through axis 33, FIGURE 1, to a reduced scale;

FIGURE 4 is a cross-sectional view through axis 44, FIGURE 1, to a reduced scale;

FIGURE 5 is an axial cross-sectional view through the axis of the tube at the ring magnets and showing in diagrammatic form the magnetic field pattern obtained;

FIGURE 6 is a somewhat diagrammatic view of the deflection mechanism in exploded condition; and,

FIGURE 7 is a somewhat diagrammatic view of the color image display mechanism of the type to which the present invention is applicable.

FIGURES 1, 6 and 7 are illustrative diagrams showing the color cathode ray tube construction to which the apparatus of the present invention is applicable, together with the ray beam deflection system. As shown in FIGURE 1, the tube is defined by an envelope having a neck portion 10, a flaring bell portion 12, and a viewing screen 14. All are symmetrical about the axis XX. A plurality of electron guns 16 (normally three) are located in the neck of the tube and generate electron beams directed towards the viewing screen 14. These electron guns are oriented to produce ray beams parallel to the axis XX and in positions to define equally spaced elements of a cylinder coaxial with the axis XX. With three guns, for example, the respective ray beams form the corners of an equilateral triangle in the planes normal to the axis XX of the tube. Two ray beams, 18 and 18a are shown in FIGURE 1 extending from the guns 16 to the viewing screen 14.

At the base of the bell portion 12 of the tube, there is provided a deflection yoke, indicated at 20. This yoke may be in various forms. One is shown in exploded, diagrammatic, view in FIGURE 6. As shown, it compromises a magnetic core 20a having an opening 20b which telescopically receives the neck of the tube as indicated diagrammatically in FIGURE 1. In addition, the yoke 20 has a pair of horizontally oriented vertical deflection windings 20c. These receive the vertical scanning current flow to deflect the ray beams periodically in the vertical direction. This is accomplished by means of a saw tooth current wave normally having a relatively low repetition rate, such as 60 repetitions per second. The deflection yoke also has a pair of vertically oriented horizontal deflection coils 20d. These receive a saw tooth current to sweep the cathode ray electron beams in the horizontal direction as required for scanning purposes. These coils normally receive a relatively high repetition rate saw tooth current wave, such as about 15.7 kcs. per second.

In use, the windings 20c and 26d carry the saw tooth current waves required to deflect the electron beams in the desired scanning pattern. The ray beams all pass through the opening 20b of the core 20a and are accordingly acted upon in unison by the time varying magnetic fields. This causes the ray beams to be deflected in unison as shown in FIGURE 1, the amount of such defiection in the vertical direction and the horizontal direction varying with time so as to cause the ray beams to trace the image area in a scanning pattern. The actual deflections of the ray beams in this fashion are essentially the same and cause the ray beams to converge'on the viewing screen at all points of deflection.

As the ray beams approach the viewing screen 14, they reach the same from difierent initial positions in relation to the axis X--X. Consequently, they reach the viewing screen along paths of travel that differ slightly from each other. This is shown in exaggerated fashion in FIGURE 1 by the two ray beams 18 and 18a. It is shown in diagrammatic perspective in FIGURE 7, where three ray beams, 18a, 18b, and 180 are shown.

The viewing screen 14 has a plurality of complementary arrays of phosphor dots, the dots of each array producing illumination of a different color when struck by the electrons. These arrays are shown in diagrammatic perspective view in FIGURE 7, one array being indicated at 14a, another by 141), and another by It will be noted from FIGURE 7 that a shadow mask or apertured plate 22 having apertures 22a is disposed immediately in front of the viewing screen 14 and in the path of travel of the electrons from the electron guns to the viewing screen. As also illustrated diagrammatically in FIGURE 7, each opening 22a serves to shield the ray beams in such fashion that they reach phosphor dots of a triad or color group made up of dots 14a, 14b, and 140 when they travel through one of the openings 22a from the respectively different initial points determined by the positions of the cathode ray guns.

It will be apparent from the foregoing that the color television image display system indicated diagrammatically in FIGURES 1, 6, and 7, is theoretically capable of causing the ray beams from the electron guns 16 to travel through the shadow mask 22 and impinge upon the viewing screen 14 in such fashion that each electron gun illt1- minates the phosphor dots of one array.By varying the intensity of each ray beam in accordance with the desired intensity of the image in that color as the ray beams scan the image, and by causing the ray beams to scan the image in unison by appropriate energization of the deflection yoke 20, the respective arrays of colored phosphor dots are caused to produce illumination of their re- 'spective colors. The resulting registered colored images are coalesced in the eye of the observer to form a single image in full color.

The color selection ability of the apparatus above described depends upon the direction of arrival of each of the ray beams 18a, 18b, and at each of the openings 22a of the shadow mask. Accordingly, any deviation from the desired paths of travel degrades the color purity of the image. As a practical matter such deviations are inevitable for a number of reasons. One reason is the magnetic field of the earth, which varies in direction and intensity at different places. Another is ambient magnetic fields due to other apparatus, which likewise may alter the direction of travel of the ray beams. Another source of difficulty is constructional variations and tolerances required in the cathode ray tube itself and the focussing and related adjustments provided therein. Because of these and other problems, it is desirable in a practical color television receiver to provide a means for adjusting the positions of the ray beams in unison and at all sweep positions, thereby to restore the theoretical action de' scribed above with reference to FIGURES l, 6, and 7.

FIGURES 2, 3 and 4 indicate how the apparatus of the present invention serves this function. As shown in FIGURE 2, a pair of permanent magnet rings 24 and 26 are located on the side of the yoke 20 towards the viewing screen 14. Each of these rings is adhesively or otherwise affixed to the face of an annular support member 28 and 30, respectively. These support members may be of fiber board or other suitable supporting material. They have, respectively, ears 28a and 30a by which they can be hand rotated in unison to vary the orientation of the magnetic field that they produce or in relation to each other to vary the intensity of that magnetic field. As seen best in FIGURE 3, the respective rings 24 and 26 may, if desired, be defined by C-shaped segments. The rings 24 and 26 are made of a suitable permanent magnet material, preferably having high permanence, good resistance to degaussing effects, high re:

sistivity, and a permeability of about 1 (permitting the same to be placed close to the deflection yoke without influencing or being influenced by the yoke). Ferrite materials combine these characteristics and are, therefore, preferred. Alternatively, other permanent materials may be used, such as Cunife, high carbon wire, flat carbon steel and the like.

The magnets 24 and 26 are magnetized diametrically, I

that is in such fashion that each ear, 28a and 30a, for example, defines the approximate position of a north pole and the diametrically opposed point defines the approximate position of a south pole, as indicated at N and S, FIGURE 3. The specific position of the poles in relation to the ears is, of course, arbitrary and may be varied as desired. The rings 24 and 26, therefore, define magnetic fields that extend through the neck 10 and adjacent portion of the bell 12 of the tube. The magnitude of the total field defined by the two rings 24 and 26 is determined -by their orientation in relation to each other, the field having maximum value when the poles of the two rings have like positions and having minimum value when the poles are in opposition to each other. In a practical unit, the maximum field attained on the axis of the cathode ray tube was about 3.0 gauss. At intermediate relative positions of the ears 30a and 28a (and hence the magnet rings 25 and 26a) the total field produced is between the maximum and minimum values. The orientation of the combined field produced by magnets 24 and 26 is determined by the orientation of the rings together about the axis of the tube, the axis of the field being substantially on a line drawn through the axis and points half-way between the north poles of magnets 24 and 26 and half-way between the south poles thereof.

In an actual construction found satisfactory, the rings 24 and 26 were of about 7 /2 inches inner diameter, 8 inches outer diamter and inch in axial length. The rings 28 and 30 were of fibenboard of about $5 inch thickness, spacing the rings in the axial direction a distance of about inch. The inner diameters of the rings 24 and 26 were about five times the diameter of the tube neck 10. The nature of the magnetic field produced within the tube is shown in FIGURES. This figure is taken on the plane normal to the tube axis and between rings 24 and 26. The diagram of FIGURE 5 is based on the disposition of iron filings on a card overlaying one of the magnets. The blank ring-like portion indicates the ring position. It will be observed that the lines of force are curved but within the confines of the tube neck (the same being indicated at 10) lines are nearly parallel and nearly straight although having some pincushion" effect.

Inboard of the support rings 28 and 30, there is a cylindrical saturable magnetic sleeve 32. In an actual unit, this sleeve was made about seven inches in diameter and seven eighths of an inch in axial length. It had a thickness of less than a sixty-fourth of an inch. Preferably this sleeve 32 is made of a material having low retentivity, high permeability and high resistivity. The latter characteristic is desirable because the sleeve 32 is relatively close to the deflection yoke and accordingly is subjected to the high frequency field produced thereby. A typical sleeve material is a saturable magnetic material that is capable of saturating when the ears 28a and 30a are moved to produce a substantial proportion of the maximum field that the rings 24 and 26 are capable of producing, but does not saturate when the rings 24 and 26 are in their opposing positions wherein minimum field is produced. The specific material and dimensions required in any given application varies in accord with the strengths of magnets 24 and 26, the distance sleeve 32 is inboard the same, and similar factors. In any specific instance the material and dimensions may be deterined by trial and error, the criterion of selection being a sleeve that serves as an effective shield when rings 24 and 26 are adjusted for minim-um field and saturates when the rings are adjusted to produce a substantial portion (e.g. 20 percent) of their maximum field. Materials that have proven satisfactory for this purpose are known as Armco Trancor XXX and 6218 type magnetic material but other saturable magnetic materials including silicon steel may be used.

It will be observed that the sleeve 32 serves not only as a saturable magnetic shield when the rings 24 and 26 are in magnetic opposition but, in addition, the sleeve acts as a central bearing for the inner peripheries of the support rings 28 and 30. The sleeve 32 thereby sustains the rings 28 and 30 in coaxial position, while permitting their independent or inunison rotations as desired.

A magnetic shield 34, FIGURES 2 and 4, is located on the bell 12 of the tube adjacent the unit defined by magnetic rings 24 and 26, sleeve 32 and support rings 28 and 30. The shield 34 is preferably of conical con struction, as shown, and is shaped to conform to the portion of the bell 12 against which it rests. As will be ap parent from FIGURE 1, the ray beams during the course of sweep approach the bell 12 of the cathode ray tube in the position of maximum sweep. They accordingly approach the magnets 24 and 26 more closely in this region than when they travel through the axial position of the magnets 24 and 26. It has been found that because of this close approach, the angle between the ray beam travel and the tube axis, and the varying axial component of field direction from magnets 24 and 26, the effect of magnets 24 and 26 varies with sweep position. This is quite undesirable, because an adjustment can then be proper only for a specific sweep position and at other positions color impurity takes place.

The magnetic shield 34 is disposed on the bell 12 of the tube adjacent the positions where the ray beam most closely approaches magnets 24 and 26. The shield 34 is preferably made of a magnetic material charcterized by high resistivity, high permeability and low retentivity. Various magnetic materials may be provided with these characteristics. Armco Trancor type XXX material has been used and found satisfactory. Other materials that may be used include what is known as 6218 type magnetic material, silicon steel, carbon steel, and the like. The thickness and length of the shield 34 are chosen to provide the requisite freedom of the ray beams from the influence of the magnets 24 and 26. In an actual construction, for example, a shield having about 7 inches inner diameter and 9 inches outer diameter was used. The length of the shield was about the axial length of the unit defined by rings 24 and 26, as shown. The thickness of the material was about .007 inch. These dimensions are not, however, critical and may be varied as necessary to provide desired degree of uniformity of action of the magnets 24 and 26.

Apparatus constructed in accordance with the present invention has proven to be highly effective. Using the dimensions listed by way of illustration above, it has been found possible to produce a negligible field within the tube neck when the magnets 24 and 26 are adjusted to produce the minimum field. This should be compared to the maximum field of about 2 gauss, giving a beam landing displacement of 0.005 inch, that would result from a construction not including the saturable sleeve 32. A 0.0005 inch minimum displacement is sufficient to cause substantial color change, and hence to impart an undesirable color impurity in a receiver that requires no correction. Moreover, with the shield 34 in place it has been found that the beam landing displacements produced by adjustments of the rings 24 and 26 are substantially uniform and the same at all positions of beam sweep. This is important since variations in this displacement at varying sweep positions requires that color imperfections at some points in the image must be accepted.

The saturable sleeve 32 and the shield 34 may, if desired, be combined in a single structure or one may be used without the other to provide some of the action of both. This results from the fact that the shield 34 is in a region of relatively low flux density, and hence is not subjected to the relatively intense field directly within the rings 24 and 26. Consequently, the same material may effectively saturate as required of the sleeve 32 and remain unsaturated in the region of the bell 12 as necessary to provide the shielding effects discussed above.

The construction of the present invention, in net effect, provides an adjustable field, transverse to the tube axis X-X, which exerts an influence on the ray beams only over a relatively short axial distance. On the electron gun side of the magnets 24 and 26, the core 20a of the yoke serves as a shield to prevent action of the magnets 24 and 26 on the ray beams. On the viewing screen side of the magnets 24 and 26, the unit 34 serves as a shield. We have found, surprisingly, that by confining the action of magnets 24 and 26, a relatively short axial distance is possible to shift the landing points of the ray beams in like amounts at all points of deflection and thereby to overcome, uniformly, the influence that otherwise would degrade color purity.

The apparatus here shown and described permits purity control by axial movement of the deflection yoke, when desired. In such instance, the yoke and the magnets 24 and 26, together with the associated apparatus, are preferably moved in unison, thereby maintaining the shielding effect of the core 20a.

While we have shown and described a specific embodiment of the present invention, it will of course be understood that modified constructions and alternatively embodiments may be made without departing from the true spirit and scope thereof. We therefore intend by the appended claims to cover all modifications and alternative constructions as fall within their true spirit and scope.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A color television image display mechanism for use with a color cathode ray tube of the type having an axis, a plurality of electron guns spaced from the axis and effective to produce cathode ray beams initially parallel to the axis and in the same direction therealong, and a viewing screen on the axis and in the path of the electron beams from said guns, said cathode ray tube further having phosphors on the viewing screen disposed in complementary arrays of dots equal in number to said electron guns and means interposed between the phosphors and the electron guns effective to cause the phosphor dots of each array to be illuminated by electrons from the electron guns respectively when the electrons approach the viewing screen from predetermined directions, whereby the ray beams produce image elements of their respective colors when they approach the viewing screen from said predetermined directions, said mechanism including;

a cathode ray beam deflection mechanism positioned between the electron guns and the viewing screen, said mechanism producing time varying fields crosswise of said axis to sweep the ray beams in unison in a scanning pattern, whereby the ray beams in unison are scanned in a pattern defining an image at the viewing screen and flaring as the viewing screen is approached from the electron guns, said deflection mechanism including a magnetic core encircling the ray beams between the viewing screen and the electron guns and prior to substantial deflection of the ray beams;

a color purity mechanism adjacent the magnetic core and on the side thereof nearest the viewing screen, said color purity mechanism including a pair of ring magnets of substantially large diameter than the diameter of said magnetic core and having substantially identical degrees of diametral magnetization, said ring magnets being adjacent to each other and coaxially disposed about the axis of the tube. said ring magnet being individually rotatable about the axis of the tube, whereby a field of adjustable intensity and orientation is provided within the tube and is effective on the ray beams after deflection; and a magnetic shield encircling the ray beams on the side of said color purity mechanism nearest the viewing screen, said shield being generally conical in shape and extending along the regions of travel of the electron beams where they most closely approach the ring magnets when under maximum deflection.

-2. A color television image display mechanism for use with a color cathode ray tube of the type having an axis, a plurality of electron guns spaced from the axis and effective to produce cathode ray beams initially parallel to the axis and in the same direction therealong, and a viewing screen on the axis and in the path of the electron beams from said guns, said cathode ray tube further having phosphors on the viewing screen disposed in complementary arrays of dots equal in number to said electron guns and means interposed between the phosphors and the electron guns effective to cause the phosphor dots of each array to be illuminated by electrons from the electron guns respectively when the electrons approach the viewing screen from predetermined directions, whereby the ray beams produce image elements of their respective colors when they'approach the viewing screen from said predetermined directions, said mechanism including:

a cathode ray beam deflection mechanism positioned between the electron guns and the viewing screen, said mechanism producing time varying fields crosswise of said axis to sweep the ray beams in unison in a scanning pattern, whereby the ray beams in unison are scanned in a pattern defining an image at the viewing screen and flaring as the viewing screen is approached from the electron guns, said deflection mechanism including a magnetic core encircling the ray beams between the viewing screen and the electron guns and prior to substantial deflection of the ray beams;

a color purity mechanism adjacent the magnetic core and on the side thereof nearest the viewing screen, said color purity mechanism including a pair of ring magnets of relatively large diameter in relation to the diameter of said magnetic core and having substantially identical degrees of diametral magnetization, said ring magnets being individually rotatable about the axis of the tube, whereby a field of adjustable intensity and orientation is provided within the tube and is effective on the ray beams after deflection;

a magnetic shield encircling the ray beams on the side of said color purity mechanism nearest the viewing screen, said shield being generally conical in shape and extending along the regions of travel of the electron beams where they most closely approach the ring magnets when under maximum deflection, and a saturable magnetic shield disposed within said magnet rings adjacent their inner edges and effective to saturate when the rings are rotated in relation to each other by amounts producing a substantial proportion of the maximum field that they are capable of producing.

3. A color television image display mechanism for use with a color cathode ray tube of the type having an axis, a plurality of electron guns spaced from the axis and effective to produce cathode ray beams initially parallel to the axis and in the same direction therealong, and a viewing screen on the axis and in the path of the electron beams from said guns, said cathode ray tube further having phosphors on the viewing screen disposed in complementary arrays of dots equal in number to said electron guns and means interposed between the phosphors and the electron guns effective to cause the phosphor dots of each array to be illuminated by electrons from the electron guns respectively when the electrons approach the viewing screen from predetermined directions, whereby the ray beams produce image elements of their respective colors when they approach the viewing screen from said predetermined directions, said mechanism including:

cathode ray beam deflection mechanism positioned between the electron guns and the viewing screen, said mechanism producing time varying fields cross-wise of said axis to sweep the ray beams in unison in a scanning pattern, whereby the ray beams in unison are scanned in a pattern defining an image at the viewing screen and flaring as the viewing screen is approached from the electron guns;

a color purity mechanism adjacent the deflection mechanism and on the side thereof nearest the viewing screen, said color purity mechanism including a pair of ring magnets of relatively large diameter in relation to the spacing of the electron guns in a plane normal to the tube axis and having substantially identical degrees of diametral magnetization, said ring magnets being individually rotatable about the axis of the tube, whereby a field of adjustable intensity and orientation is provided within the tube and is effective on the ray beams after deflection;

a magnetic shield encircling the ray beams on the side of said color purity mechanism nearest the viewing screen, said shield being generally conical in shape and extending along the regions of travel of the electron beams where they most closely approach the ring magnets when under maximum deflection; and

a saturable magnetic sleeve disposed within said magnet rings adjacent their inner edges and eflective to saturate when the rings are rotated in relation to each other by amounts producing a substantial proportion of the maximum field that they are capable of producing.

References Cited by the Examiner UNITED STATES PATENTS 2,860,329 11/ 1958 Reiches 313-75 X 3, 106,65 8 10/ 1963 Chandler et a1. 313-77 FOREIGN PATENTS 480,567 4/ 1954 Italy.

JAMES W. LAWRENCE, Primary Examiner.

V. LA FRA'NCHI, Assistant Examiner. 

1. A COLOR TELEVISION IMAGE DISPLAY MECHANISM FOR USE WITH A COLOR CATHODE RAY TUBE OF THE TYPE HAVING AN AXIS, A PLURALITY OF ELECTRON GUNS SPACED FROM THE AXIS AND EFFECTIVE TO PRODUCE CATHODE RAY BEAMS INITIALLY PARALLEL TO THE AXIS AND IN THE SAME DIRECTION THEREALONG, AND A VIEWING SCREEN ON THE AXIS AND IN THE PATH OF THE ELECTRON BEAMS FROM SAID GUNS, SAID CATHODE RAY TUBE FURTHER HAVING PHOSPHORS ON THE VIEWING SCREEN DISPOSED IN COMPLEMENTARY ARRAYS OF DOTS EQUAL IN NUMBER TO SAID ELECTRON GUNS AND MEANS INTERPOSED BETWEEN THE PHOSPHORS AND THE ELECTRON GUNS EFFECTIVE TO CAUSE THE PHOSPHOR DOTS OF EACH ARRAY TO BE ILLUMINATED BY ELECTRONS FROM THE ELECTRON GUNS RESPECTIVELY WHEN THE ELECTRONS APPROACH THE VIEWING SCREEN FROM PREDETERMINED DIRECTIONS, WHEREBY THE RAY BEAMS PRODUCE IMAGE ELEMENTS OF THEIR RESPECTIVE COLORS WHEN THEY APPROACH THE VIEWING SCREEN FROM SAID PREDETERMINED DIRECTIONS, SAID MECHANISM INCLUDING; A CATHODE RAY BEAM DEFLECTION MECHANISM POSITIONED BETWEEN THE ELECTRON GUNS AND THE VIEWING SCREEN, SAID MECHANISM PRODUCING TIME VARYING FIELDS CROSSWISE OF SAID AXIS TO SWEEP THE RAY BEAMS IN UNISON IN A SCANNING PATTERN, WHEREBY THE RAY BEAMS IN UNISON ARE SCANNED IN A PATTERN DEFINING AN IMAGE AT THE VIEWING SCREEN AND FLARING AS THE VIEWING SCREEN IS APPROACHED FROM THE ELECTRON GUNS, SAID DEFLECTION MECHANISM INCLUDING A MAGNETIC CORE ENCIRCLING THE RAY BEAMS BETWEEN THE VIEWING SCREEN AND THE ELECTRON GUNS AND PRIOR TO SUBSTANTIAL DEFLECTION OF THE RAY BEAMS; 